The primary aim of our research project is to elucidate the regulatory mechanism for cholesterol metabolism in brain tissue. The change in brain HMG CoA reductase activity during development has been reported. Since it is known that the activity of hepatic HMG CoA reductase is regulated by phosphorylation and dephosphorylation of the enzyme we determined whether the activity of HMG CoA reductase in brain is also regulated by the mechanism similar to that in liver. Results of our studies indicated that phosphorylation of the HGM CoA reductase in brain reduces the enzyme activity and that dephosphorylation increases the activity. We plan to examine if the change in HGM CoA reductase activity during development is related to the phosphorylated or dephosphorylated form of the enzyme. We will also determine whether the activity of phosphatases in brain show an age dependent alteration during development. Another aspect of this project is to evaluate the role of cholesterol esters and the ester metabolizing enzymes in the processes of myelination and demyelination. To attain this we examined the activity levels of the ester metabolizing enzymes in brain tissue from patients with various demyelinating diseases. The data indicated that the increase in cholesterol ester concentrations in brain from patients with multiple sclerosis may be related to a reduction in the ester hydrolase activity. The presence of cholesterol esterifying enzyme and the ester hydrolase activity in cerebrospinal fluid (CSF) was also recently reported by us. We plan to assay CSF from MS and non-MS patients for cholesterol ester concentrations and the ester metabolizing enzymes. We will also determine the activities of cholesterol ester metabolizing enzymes in brain tissue from myelin deficient mutant mice (Quaking and Jimpy) and correlate the change in enzyme activity with cholesterol ester concentrations.